Urban Energy Evaluation of Energy Design

1
Urban EnergyEvaluation of Energy Design

• Henrik Sørensen - Niels-Ulrik Kofoed
• Esbensen Consulting Engineers
• Sukkertoppen Copenhagen
• Carl Jacobsens Vej 25D, DK-2500 Valby
• Tel. [phone], Fax. [phone]
• e-mail h.soerensen_at_esbensen.dk

2
Background

• This evaluation is carried out based on the
  competition material by the design team of Urban
  Energy and comments by NBI and SINTEF
• Aim of this evaluation is to provide an overview
  of the suggested design and evaluate the overall
  energy design in terms of energy aspects and
  thermal indoor climate
• Secondly a number of important issues to consider
  if the project is going to be realised will be
  pointed out, and some ideas and recommendations
  on how to deal with these issues are provided

3
Generally regarding the competition

• Conditions
• The brief of the competition suggest the design
  teams to provide innovative solutions focusing on
  substantially, reduced energy consumption and
  maintaining high level of indoor climate
• In the evaluation of the incoming proposals a
  standard calculation tool Energi i Bygninger
  should be used to evaluate the design and the
  design teams have to provide information
  accordingly
• The choice of simulation tool is a balance of
  having a sufficiently detailed tool to be able to
  compare the projects and sufficiently simple tool
  to ask the design teams to use in their
  competition entries which is an reasonable effort
  to demand from the teams

4
Generally regarding the competition

• Problem with these conditions
• Potentially the problem in this procedure, that a
  design team can pursue good calculation results
  in a simplified program that do not reflect the
  real performance of the suggested design
• The standard tool is not capable of taking into
  account the very dynamic energy flows of the
  proposed design and results will be almost
  entirely dependent on the assumptions made
• In the practical evaluation of the competition
  entries this means that the specialties of the
  individual designs are very difficult to compare
  and the differences between the projects are
  leveled out

5
Design team calculations

• The design team of Urban Energy has used a Danish
  simulation program BV98 to document the
  energy-profile of the Urban Energy project
• Danish weather data has been used as climatic
  conditions for this calculation, however this
  implies a general underestimation of the energy
  consumption needed for heating by approx. 20,
  since a Norwegean weather data set has 20 more
  degree-days than Copenhagen and e.g. average
  temperatures in the coldest months are several
  degrees lower in Oslo than Copenhagen
• The Danish tool has the same level of detail as
  the standard tool for the competition, but this
  also means that the dynamic effects pointed out
  in the following, has not been taken into account
• In general the calculations by the design team
  underestimate the energy consumption if the
  building would be realised directly based on the
  sketch design presented by the design team

6
General comments on the concept

• The project consider a number of the right key
  parameters, which contribute to the reduction of
  the total energy consumption of the building
• Daylighting
• Solar shading
• Natural ventilation
• Thermal mass to even out temperature fluctuations
• Building envelope with low transmission losses
• The use of atria to provide driving forces for
  natural ventilation
• Supplementing fans to be used under conditions
  where natural ventilation cannot provide
  sufficient ventilation
• Potentially the suggested architectural design
  and a careful energy design with focus on the
  above issues could lead to a new and important
  step forward in demonstrating a new generation of
  energy efficient commercial developments in Norway

7
General comments on the concept

• However the documentation of the project is quite
  poor and generally no considerations on the
  variations of thermal indoor climate in various
  parts of the building are considered regarding
• Wind
• Solar radiation, especially glare
• Stack effects in the atrium providing very
  different conditions at ground floors and top
  floors
• The influence of outdoor climate conditions in
  winter regarding draught from incoming air
• Modes of operation (cold, hot, wind, no wind
  etc.)
• Fire safety strategy (smoke) is not elaborated
• Control strategies, components, systems and
  related energy consumption for this is not
  elaborated

8
Daylighting proposed design

• The strategy of reducing building depth provide a
  good starting point for saving energy for
  artificial lighting.Some issues however reduce
  the potential of this saving
• In the double facade the horizontal division will
  result in an relatively large overhang due to the
  high level of insulation of each floor reducing
  the amount of daylighting in the depth of room
• The solar shading is not supplemented with a
  glare protection, which will be needed in
  practise to allow for work on PCs. Due to the
  very large glazed area of the facade the glare
  protection will be needed in large parts of the
  working hours (also at times when there is no
  direct sun on the facade).
• This will lead to increased use of artificial
  lighting also to compensate for the glare from
  large differences in luminance of surfaces close
  to the facade and in the depth of the rooms.

9
Daylighting if realised

• Important to perform detailed simulation of the
  daylighting conditions for situations facing a
  free facade and towards the atrium
• Glare protection should be incorporated in facade
  design and the facade design should be detailed
  to allow more daylighting from the highest part
  of the windows on each floor and have different
  conditions for lower part.
• This would allow glare glare protection but at
  the same time allow daylight to penetrate deep
  into the building, maximise the use of
  daylighting for lighting and saving electricity
  for lighting.

10
Ventilation proposed design (1)

• The general ventilation concept is based on cross
  ventilation with incoming air from the facade and
  exhaust through the atrium
• No additional height is suggested in the atrium
  as buffer for smoke and the plume of hot air and
  smoke rising in the atrium.
• Potentially this means a very difficult smoke
  ventilation situation and a general problem for
  achieving approval of the fire safety in the
  building

11
Ventilation proposed design (2)

• Furthermore this means that the neutral-line for
  the pressure distribution in the atrium will be
  inside the building.
• This implies in practise that a large part of the
  normal operation hours of the building, there
  will be a over-pressure from the top of the
  atrium to the top floors, pushing hot air from
  the atrium into these floors.
• Especially in summer this will be a problem
  providing a serious risk of overheating of all
  top floors of the building.
• The same condition will also happen in all
  situation where the doublefacade is opposite to
  the wind direction. This will lead to
  underpressure on the facade and hot air from the
  atrium will be sucked into the floors or just
  balance the pressure resulting in no ventilation
• The suggested supplementing fans will not be
  sufficient to compensate this effect in the open
  plan solution for the floors

12
Ventilation proposed design (3)

• The incoming air is expected to be provided to
  each floor through the double-facade but no
  temperature control of the incoming air is
  suggested.
• Summer
• In summer, the suggested ventilation strategy
  will result in a situation where all heat from
  the solar shading located in the double facade
  will be ventilated into the building in stead of
  being ventilated to the outside of the building
• In practical terms this means that the solar
  shading will act like an interior solar shading
  (all heat goes to the indoor air).
• With the very high glazing ratio and fully solar
  shaded facade this will lead to substantial solar
  gains which cannot be compensated with the
  suggested thermal mass or natural ventilation
• Winter
• In winter the supply air will only to a very
  limited level be preheated in the double facade
  and given the outdoor condition in the cold
  months in Norway, major discomfort from draught
  due to the low temperature of the incoming air
  must be expected.

13
Ventilation if realised

• The ventilation strategy of the building would
  need to be redesigned for the various modes of
  operation
• Atrium should be design allowing for smoke
  buffer-zone and moving the zero pressure line of
  balance outside the building. This would ensure a
  reduction in the number of hours with to high
  pressure in the top floors of the atrium
• Double facade should be designed with focus on
  protecting the solar shading and allowing hot air
  to be ventilated to the outside in summer
  conditions
• Incoming air in winter should be preheated and
  various components for this already exist on the
  market which can be combined with low-temperature
  heating system (to compensate the down-draughts
  from windows) and has very low pressure drop, so
  the ventilation strategy with fresh air can be
  maintained
• Simulation of the various modes of ventilation
  should be carried out with CFD or similar
  advanced tools at an early stage of the detailing
  of the design

14
Conclusion

• On the competition
• Launching a competition asking for advanced
  designs needs also to include evaluation with a
  relative advanced design tool, and asking the
  competing groups to give a complete description
  of their entries regarding modes of operation
  combining
• Winter, summer, autumn/spring
• Hot day / cold day
• High wind / low wind from different directions
• Especially in high buildings also differences in
  mode of operation on top floors compared to
  ground floors are crucial in the evaluation of
  the designs
• Since this has not been the case in the actual
  competition, the evaluation of projects has to be
  based as much on the potential of the project as
  the actual calculation results provided in the
  entries, since they do not reflect the real
  performance of the suggested designs.

15
Conclusions cont.

• Energy concept of Urban Energy
• In popular termsthe project has the right
  ingredients but the recipe has to be adjusted on
  a number of key issues
• Especially daylighting, ventilation and fire
  safety issues are crucial to elaborate to be able
  to realise the project
• This detailing should be done in very close
  dialogue with the client of the building to be
  based on real occupancy, internal loads,
  flexibility demands, use etc.
• Due to the complexity of the building advanced
  dynamic simulation programs are necessary to use
  already from the early design phase to design the
  solutions with respect to the different
  conditions in the various parts of the building

16
Conclusions cont.

• Provided the right detailing and optimisation the
  project has a good potential for achieving
  relatively low energy consumption and good indoor
  air quality
• The passive features of the building
  (transparancy, thermal mass, interior design,
  facade detailing) will be a crucial parameters in
  this optimisation.
• Only if the client and design team are willing to
  consider variations of the facade architecture in
  different parts of the building, redesigning
  solar shading, handling and preheating of fresh
  air, glare control, changing openings and shape
  of atrium and overall improvement of the U-value
  the targeted energy results will be achieved.

17
Contacts

• Henrik Sørensen
• Head of Branch Office
• eMBA(MMT), M.Sc. Engineering, M.FRI, M.IDA
• h.soerensen_at_esbensen.dk
• Esbensen Consulting EngineersSukkertoppen
  Copenhagen
• Carl Jacobsens Vej 25D
• DK-2500 Valby
• Tel. [phone], Fax [phone]
• www.esbensen.dk