Case Study _ UN CITY, Copenhagen

The building for UN CITY in Copenhagen was completed in 2013 and it boasts some impressive green building aspects.

 

Shaped as an 8 pointed star, the building houses 1700 staff in 9 departments. Architects 3XN ensured that energy efficiency was maximized by employing these clever solutions:

• The central feature staircase connect the different wings of the building and encourages interaction among the staff… positive engagement and discussion is obviously a key component of the UN.

• Reclaimed land – an artificial island on the harbor ensures that existing valuable greenfield land was not used.

Context: The 8 pointed star on reclaimed land

HEATING & COOLING

• External aluminium solar shutter are controlled by workers from their computers. Perforations in the shutters ensure that daylight still permeates even as direct solar gain is excluded.
• Sea water is pumped into the buildings network of pipes to COOL the building, which almost eliminates the need for any mechanical cooling.
• A white recyclable membrane coats the roof which reflects solar gain to further assist cooling of the internal work environments

BUILDING FABRIC

• High U-values of building materials ensure that external envelope is well insulated.

ENERGY USAGE:

• Solar PV panels generate 297,000 kWh/yr. Approximately 1400 panels are located on the roof.

WATER CONSERVATION:

• aerator taps reduce water usage
• Rainwater is collected and used to flush toilets. Approximately 3000000 litres are collected annualy which is almost all the required water for the flushing of toilets.

LIGHTING

• low energy light fittings
• daylight is maximized via open plan layouts, which also allow flexibility in function – future-proofing.

 

AIR QUALITY

• outside air is filtered for indoor use, regulating humidity and ensuring a constant fresh supply.
• Chemicals and other pollutants are minimized through selection of construction and furniture materials.

Overall energy consumption is incredibly low at 50kWh/m2. When compared with the average commercial building consumption in the UK, this is exceptionally good:

Energy use indices (EUIs) for good practice and typical examples of the four office types (Source)

UN City would classify in the catogory number 4 – Prestige, air-conditioned which suggests typical consumtion of 560kWh/m2/yr, or good practice of 350kWh/m2/yr.

The building is LEED Platinum certified and was awarded the European Commision’s Green Building Award in 2012.

CREDITS
Location: Copenhagen, Denmark
Client: FN Byen (Copenhagen Port & City Development)
Gross Floor Area: 52.000 m²
Cost of Construction: 134.000.000 Euros
Architects: 3XN
Interior Design: PLH / UN Common Services
Contractor: E. Pihl & Son
Consultants
Engineering: Orbicon
Landscape: Schønherr

The beauty of Rammed Earth

There is something about rammed earth walls that really appeals to me. The rich colour and texture of the compacted earth links the building so well with the natural surrounds – from which the soil should ideally come. The solid bulk of the walls has an anchoring, permanent effect that connects well with the concept of ‘Sheltar’. Rammed earth has been used for millenia as a solid, durable and thermally massive.

Traditional rammed earth construction in North Africa

Rammed earth construction in modern design

It may also be surprising to you that this type of construction has been used on all continents. It was to me… I would have thought that very wet climates would not be suitable but if the walls are sealed and internal reinforcements, such as bamboo, are used, the walls can last for centuries. Reinforcing the walls is also important for areas prone to earthquakes.

Timber reinforcement to rammed earth walls

The composition of rammed earth walls are a damp mixture of earth (containing gravel, sand and clay). Lime is frequently used as a stabilizer, historically animal blood was used, and in modern times cement is often favored. In an effort to used waste as a construction material, one could also add bits of old tyres and glass to create variety and texture.

 

More recently, rammed earth walls are often build off of concrete foundations to provide a more durable base. 

Technical diagram showing rammed earth foundation on conventional footing

So how is the wall actually constructed? Well shuttering is created using plywood or metal panels. These are clamped together a set distance apart to avoid bulging. Them the earthy mixtured is added 10 – 25mm thickness at a time, and compressed to roughly half the original height. This is what results in the lovely horizontal lines that are typical of rammed earth walls. 

Rammed earth wall texture

Construction should be undertaken in the summer to maximize the warmth that assists the drying out of the walls. The curing process can take up to two years but the walls will be pretty rock hard almost as soon as the shuttering is removed.

Wall construction steps

In wet climates, the walls should be suitably covered with wide eaves or used internally, this is because over time, rain will erode the walls.

Technical detail at eaves

The process is labour intensive as each layer is physically ‘rammed’ into place. The cost though are very low and this is why it has been a favored method of construction around the world. Although it is not a strong as concrete, it achieves compressive strengths of about 4.3Mpa which is more than suitable for domestic buildings.

Rammed wall construction in progress

Rammed earth walls have a low embodied energy as almost all the material required should be sourced from the site, and unless a mechanically operated tamper is used to compress the soil, no electrical source is required.

 

The beautiful finish looks fantastic in modern construction, as natural as it does in very basic, traditional construction.

Contemporary design using rammed walls

 

In addition to the energy efficient, low-carbon construction, the thermal mass helps to regulate indoor temperature. Particularly good for hot climates as the external heat is absorbed into the thick walls and released to the cool night sky. For cold climates, insulation such as xpanded or extruded polystryrene will be good to retain warmth inside the building.

Layer of insulation in rammed wall. Good practice in colder climates.

The natural colours of the earth make for a beautiful finish

 

LCT: Greywater systems

1 in 3 people (2.5 billion of the worlds population) do not have access to safe water and sanitation. Source: (wateraid.org). As demand for water increases, it is increasingly difficult to maintain the supplies of water to meet the needs of a growing population. On average, a person will use 150 litres per day (see graph below). Sustainable design guidelines recommend that fittings and fixtures reduce this to 80l/p/d through the installation of dual flush toilets and low flow taps and showers. One of the best options is to make use of greywater systems. In areas like the UK where there is high rainfall almost all the year round,greywater systems are less common than drier climates where, in my opinion, it should be a crime not to have a waterrecycling system in every building.

Greywater systems effectively collect wastewater from baths / showers / wash hand basins and washing machines, and use this water to flush toilets and irrigate gardens. (Waste water from toilets and kitchen sinks is classified as BLACK water and must be heavily treated prior to reuse).

Greywater systems collect water and filter it through a series of stages. A septic tank of sorts contains the water and allows solids to settle, while the ‘overflow’ is then filtered – gravel and bentonite clay are some common filtration stages. Thus particles are removed and the filtered water is pumped out for irrigation or into a toilet cistern.

The following list is sourced from www.greywatersystems.co.za :

The pros are:

• Higher savings for everyone
• Good and continuous irrigation
• Food supply is not interrupted
• Gardening and farm irrigation reduced to minimal or zero costs
• Demand for fresh water decreases
• Lower pumping and treatment costs

The cons are:

• Greywater cannot be stored for long or the nutrients in it will break down and it will start to smell bad.
• Quality of water may be different with high levels of boron that can destroy crop and plants
• If vegetables irrigated with contaminated water is eaten raw, it will cause health problems like diarrhoea
• Transmission of some infectious diseases through toxic chemicals from the used water to plants
• Too much nitrogen, sodium, and boron which could cause soil to degrade and groundwater to be contaminated

 

Systems like the MATALA  have in-built pads that filter the water and require no chemical treatments. UV light is used as an effective but environmentally harmless way to kill bacteria.

I do love the simplicity of the SINK POSITIVE…  This is clever design!

Problems associated with Airtight buildings

Last post I looked at the importance of airtightness when it comes to low-carbon buildings. The lower the air infiltration, the greater the thermal comfort and less heating or cooling required to keep the indoor temperature comfortable.

The dangers of air-tight buildings are three-fold:

1. POOR AIR QUALITY

• reduced fresh air into the building results in high CO2 levels which is bad for health

2. MOULD GROWTH

• warm, moist air internally – as a result of breathing / laundry/ bathing etc – cools on external walls and windows and causes condensation and mould growth

Diagram showing moisture within walls

Common sight at well sealed window frames as moist warm air cools when coming into contact with cold surface of external openings

 External wall details showing typical problems due to moisture (A,B&C) and ideal solution (D)

3. OVERHEATING

• Highly insulated and air-tight buildings are susceptible to overheating in the summer. The Chartered Institute of Building Services Engineers / Arup Study defines WARM as 25C and HOT as 28C. Designers must consider this to allow for natural ventilation solutions that incorporate opening windows and roof vents to encourage cross ventilation and stack-effect.

Older buildings often make use of air-bricks high up on external walls so that warm, moist air can escape and allow fresh air into the building. But this totally conflicts with the intention of restriction indoor – outdoor air flow to preserve indoor temperature. Air-bricks are useful where the difference between indoor and outdoor temperature is not massive, for example climates where artificial heating or cooling is not generally used. Windows typically have trickle-vents incorporated into the frames to assist with the exhaust of moist air, but these also let unwanted cold air inside.

Victorian houses were actually designed and made to be quite leaky (rattling sash windows and open floor boards) to allow the smoke from coal fires to escape in an attempt to keep air healthy, however, thermal comfort was poor due to the draughty interiors and they were expensive to heat.

There is now a serious effort to retrofit these buildings to improve air-tightness and increase building envelope insulation.

Where mechanical heating and / or cooling is required, air-tightness is vital to energy efficiency and thermal comfort. The best way of ensuring good air quality (low CO2 levels) and good humidity levels (below 60%) is to make use of MVHR – mechanical ventilation and heat recovery system.  It is also worth noting that the MVHR can be switched OFF in the summer months to allow occupants to open windows and doors to naturally ventilate the building.

Schematic of MVHR installation

MVHR is only really necessary with air change rates of less than 4 per hour. However, I live in an apartment that has about 8 air changes per hour and while we have not issue with CO2 levels – typically 1000ppm, we have a big problem with humidity levels and condensation. In winter we use a de-humidifier permanently to control moisture levels. In summer we open the windows and the natural ventilation works just fine.

In summary, designers should design air-tight buildings but must consider efficient ventilation heat recovery systems which work to ensure healthy fresh air levels and extract moist air from kitchens and bathrooms to discourage mould growth. These should be commissioned properly before occupation and filter cleaned regularly. It is also imperative that the design considers good passive ventilation during summer months when the MVHR unit can be switched off.

INTERESTING LITERATURE ON THE SUBJECT:

• Zero Carbon Hub published a ‘Practical Guide to building Air-tight buildings’
• Useful article here… ‘Build tight, ventilate right’
• Mould growth and high humidity levels are a very common problem for buildings in cold climates and increasingly uncovered as an issue in modern renovated or new airtight buildings. This article…  describes a situation in America where an office building was renovated to improve air-tightness but it because a party ground for mould growth and resulted in the building being shut down and occupants relocated due to the hazardous air quality.

USEFUL PRODUCTS:

• Aereco, a french compancy that specialises in humidity sensitive ventilation systems, uses sensor technology to switch on an off depending on humidity levels. This works well to conserve energy but ensure good air quality too. 
• MVHR system from Green building store

Airtightness – is it all just a load of hot air??

No one likes a leaky building! You may not have thought about it before but I guarantee you have felt the discomfort of being in a draughty room. Much of sustainable building design relies of appropriate building materials and the orientation of windows and openings, these are the obvious aspects that are considered towards energy efficient buildings. However, if the building is not adequately airtight, any effort you might have made for insulation and orientation will be seriously compromised. Think about it – the idea is to keep heating or cooling INSIDE but if the nice warm/cool air is simply escaping out through poorly sealed building envelope, any insulation is rendered mostly useless. So to answer the question in the title – It is all about hot (or cool) air to achieve optimum thermal comfort at minimum cost.

Typical heat-loss pathways

The diagram above shows the common spots that contribute to poor airtightness…Junctions – roofs to walls, walls to floors; and openings – doors and windows and wall penetrations for services.

Regulations and guidelines vary on the level of airtightness required. From the best (Passivhaus) at 0.6 air changes per hour (ach) at 50Pa to British building regs at 10 air changes per hour.

Maximum air permeability	(m3/(h.m2) at 50Pa*
UK Building regulations – poorest acceptable standard	10
Building regulations indicative Part L 2010 target	7
Netherlands	6
Germany	1.8 – 3.8
Energy Saving Trust best practice	3
Super E® (Canada)	1.5
PassivHaus Standard	0.6
* Some values are actually air changes per hour @ 50Pa.

Buildings have to be constructed VERY well to achieve the passivhaus requirement of 0.6 and generally require the use of special membranes and taping to minimise air leakage. Airtightness tests are conducted during construction to check where levels are at and if more work needs to be done to achieve the desired levels (see image below)

Airtightness test carried out during construction

Where a building has less than 4 ach @ 50Pa, artificial ventilation will be required or the air quality will become unhealthy. (See previous blog post on this). Great for heat retention but bad for oxygen levels! The best systems in use are the Mechanical Ventilation Heat Recovery (MVHR) which uses heat from stale air being extracted, to warm incoming fresh air. You might be thinking, whats the point of making a building so airtight if you need energy to regulate air quality. But the energy used to run MVHR is minimal and costs about 50 pence per week and when you compare this to the reduced heating or cooling demand, there is no contest.

So, what kind of design decisions are required to achieve exemplar airtightness?

During my studies, SIGA did a workshop with us to educate us about their many products and how these should be used…

SIGA workshop at Oxford Brookes University

Membranes line out the entire inside of the building and these are fixed in place with tape and double sided sticky strips. Nails or staples should never be used as the piercings would compromise the integrity of the membrane.

All openings and penetrations are taped up:

SIGA product diagram showing where the products are used on a typical house envelope

There are typically two layers of BARRIER MEMBRANES in a good roof and wall design:

1. (RED LINE) the VAPOUR BARRIER (Airtightness layer) stops warm, moist internal air from getting into through the insulation and causing mould growth.
2. (BLUE LINE) the BREATHER  MEMBRANE (Weather-tight layer) allows moisture OUT but stops weather driven air and moisture INTO the building.

It is important to note that there is a difference between AIRTIGHTNESS and AIR INFILTRATION – the former refers to gaps in the building envelope which allow valuable warm or cool air to escape. Infiltration, however, is affected by wind loads / occupant behavior / natural ventilation strategies.

Energy Savings Trust has produced a document with some good case study information regarding this subject.

Find membranes and tapes at SIGA or INTELLO.

Next post I will look at the problems associated with Airtight buildings, namely poor air quality and mould and moisture issues, and how these can be avoided.

 

Costs to achieve zero carbon buildings are falling – Zero Carbon Hub Report

One of the biggest hindrances to the construction of sustainable buildings is the extra cost incurred to achieve the improved performance. Despite the savings that one can experience during the life of the building as a result of lower energy bills, the build costs upfront are a deterrent. As building regulations improve to demand high quality, high performing, low carbon buildings, the gap between national regulations and exemplar standards (eg. Passivhaus and Code for Sustainable home level 6) is diminishing.

The LIGHTHOUSE by Sheppard Robson Architects was the first UK building to achieve zero carbon (Code for Sustainable Homes level 6) status.

ZERO CARBON HUB has recently released a report on the costs associated with Low Carbon buildings: Cost Analysis: Meeting the Zero Carbon Standard, Feb 2014. (All images and tables are extracted from the report.)

The findings are very encouraging. The results show that the additional costs associated with reaching Low Carbon buildings has roughly halved since the previous report in 2011. Additionally costs are expected to continue to fall between 2014 and 2020.

At Today’s prices, the additional cost to build a semi-detached dwelling to zero carbon standard is in the region of £5000.

The elements that contribute to the zero carbon standard are as follows:

1. Fabric Energy efficiency should contribute the greatest componant and refers to the insulating properties of the building envelope. High performance windows and openings, well insulated roofs, walls, and floors
2. Low / zero carbon technologies are used to reduce energy demand from non-renewable fuel sources (gas & coal-powered electricity). These typically include solar PV (electricity), wind turbines, Solar hot water systems, and Heat pumps (ground / air-source) etc.
3.  ‘Allowable solutions’ refer to a government scheme to offset additional carbon use by investing in projects that aim to improve carbon reduction in various industries.

Key findings of the REPORT:

• Continuing drop in costs associated with reach low carbon standard for dwellings. Particular reductions in cost estimates for Solar PV, air-tightness and thermal bridging components.
• Reasonable additional costs are found to be:
  • Detached dwelling = £6700 – £7500
  • Semi-detached = £3700 – £4700
  • Apartments (low-rise) = £2200 – £2400
• Costs will continue to fall from 2014 to 2020 – resulting in additional costs for detached dwellings = £5700 – £6300; semi-detached = £2900 – £3600; apartments = £1900 – £2000
• These costs assume the lowest capital costs associated with zero carbon standard – this requires the use of Solar PV.
• The cost of solar PV is expected to fall at a greater rate than the cost of improved building fabric solutions such that the use of PV will achieve a zero carbon solution at lower cost that a Passivhaus solution (to use an example of Advanced energy efficiency scenarios).
  • Cost of PV has dropped from around £3800 / kWp in 2010 to £1500 / kWp today.
• Table below shows a summary of cost breakdown for the 4 different housing types.

 Energy targets associated with different dwelling types:

 

This report is most encouraging as we strive to boost the number of new buildings (and retrofitted buildings) that are zero carbon. Thanks to the Zero Carbon Hub for this report and for making the costs associated with green buildings easier to interpret and therefore entertain.

Image courtesy of Zero Carbon Hub: Cost Analysis Report 2014

Rawlemon’s spherical solar energy collector

Rawlemon have designed a glass globe that tracks the sun (and moon) and concentrates the light up to 10000 times. The company claims that it is 35% more efficient than photovoltaic panels.

Rawlemon devices harness diffuse light, so they can work at night as well as during the day (Gizmag)

The sun’s energy is concentrated towards a small surface area of photovoltaic cells

See video clip here.

Sweat to energy

I have often wondered if my furious spinning workout could be of greater value that just a great cardio session. The following article provides some great answers. I recall one of my extreme ideas while working on a social housing project, I thought about the potential  for an in-house gym to generate electricity for the occupants. Dwellers would be able to discount their energy bill by the amount of energy they could generate from an exercise bike. A healthy workout AND free energy – win-win scenario… but how possible is it really??

READ ARTICLE.

In summary… A fit person would generate approximately 100 Watts per hour which is about enough to power a television for the same amount of time…

Let’s assume that the average piece of exercise equipment is in use 5 hours a day, 365 days a year. If each patron generates 100 watts while using it, that machine creates some 183 kilowatt-hours of electricity a year. Commercial power costs about 10 cents per kilowatt-hour on average in the United States, so the electricity produced in a year from one machine is worth about US $18 dollars. (quoted from article)

The cost of the equipment is around $1000 (2011) which achieves a payback of 55 years!! Not quite award winning results.

Improvements in the efficiency of the technology may make this feasible in future but for now, it’s a nicer idea than its actually worth.