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Intermediate Report on the Design and Construction of a Net-Zero-Energy Building in Muscat Oman

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Abstract and Figures

The development of energy-efficient buildings in the Gulf region is a timely and relevant task given the challenges of a very high demographic pressure, accelerating energy demands, and a hot climate. This paper is a report of the design and construction process of making the Eco House, a net-zero-energy building currently being built on the campus of the German University of Technology in Oman. The project aims at prolonging the passive operation period without the need for mechanical cooling through maximizing so-called passive design strategies; reducing the energy demand for the mechanical cooling period through maximizing so-called active design strategies; using the building to demonstrate cyclical processes for the use of water, materials, local products, native plants, and for the education of students and the wider public on sustainability in building. It is assumed that a net-zero-energy balance can be reached. Furthermore, market viability and policy conclusions are discussed.
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WORLD SUSTAINABLE BUILDING 2014
BARCELONA CONFERENCE
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Sustainable Building: RESULTS
Are we moving as quickly as we should?
It’s up to us!
CONFERENCE PROCEEDINGS
VOLUME 5! !
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Intermediate Report on the Design and Construction of a Net-
Zero-Energy Building in Muscat, Oman
Speakers:
Knebel, Nikolaus (NK)2, Rudolph, Matthias (MR)1, Werminghausen, Martin (MW)², Frenzel,
Christian (CF)1, Othmani, Rumana (RO)2, Zain, Rowa (RZ)2
1 Transsolar Energietechnik GmbH
Curiestr. 2, 70597 Stuttgart, Germany
2 German University of Technology in Oman, Department of Urban Planning and
Architecture
Muscat Express Highway, Halban, Barka. PO Box 1816, PC 130 Athaibah
Abstract: The development of energy-efficient buildings in the Gulf region is a timely and
relevant task given the challenges of a very high demographic pressure, accelerating energy
demands, and a hot climate. This paper is a report of the design and construction process of
making the Eco House, a net-zero-energy building currently being built on the campus of the
German University of Technology in Oman. The project aims at prolonging the passive
operation period without the need for mechanical cooling through maximizing so-called
passive design strategies; reducing the energy demand for the mechanical cooling period
through maximizing so-called active design strategies; using the building to demonstrate
cyclical processes for the use of water, materials, local products, native plants, and for the
education of students and the wider public on sustainability in building. It is assumed that a
net-zero-energy balance can be reached. Furthermore, market viability and policy
conclusions are discussed.
Keywords: passive and active design strategies, net-zero-energy building, solar exposure,
high performance envelope, hydronic cooling, dedicated outdoor air system, grid-connected
photovoltaic system, natural and local materials, Oman
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1. SETTINGS
Until one generation ago the housing stock in the Sultanate of Oman consisted of climate-
adapted zero-energy vernacular buildings. After the discovery of oil and gas resources and the
modern development of the country since the 1970s, the population's lifestyle and thus
comfort expectations have changed. Today, the housing stock consists of "modern"-looking
but poorly designed and constructed buildings, which are inappropriate to the climate and
consume electricity to such an extent that the government subsidies for electricity are
becoming a real challenge for the country's budget and ability to invest in future-oriented
projects (1). Oman is experiencing rapid urbanization in the form of suburbian settlement
patterns with single-family houses; 40% of the country's housing stock was built after 2006
(1). Since every adult citizen in Oman is eligible to receive a plot of land to build a house, this
trend will accelerate. Developing energy-efficient buildings, and prooving their technical
feasibility and market viability are therefore timely and relevant tasks for the country and the
Gulf region as a whole, which is facing a similar situation.
1.1. Competition
In order to promote scientific research on and public awareness of energy-efficient buildings,
The Research Council of the Sultanate of Oman (TRC) launched the “Oman Eco-Friendly
House Competition” in 2011. It grants university-led teams of academics, students, and
practitioners, as well as consultants, contractors and companies a budget to design, build,
operate, and monitor an energy-efficient building for residential use on their campuses. The
overall aim is to achieve a net-zero energy balance whilst providing a comfortable indoor
environment with the cooling set points being 25-27°C operative temperature and 50-70%
relative humidity.
The Eco House built on the campus of the German University of Technology in Oman is a
two-storey university guesthouse for visiting faculty with a net indoor area of 210m2. A
round wall embraces a rectilinear structure of four parallel walls containing all rooms. On the
ground floor are two entrances, one leading to the living room, and the other to the dining
room, in-between are the kitchen, a technical room and a restroom. On the upper floor are
three bedrooms, each with an attached bathroom. The basic layout could be translated into a
house to be occupied by a family of four people. Since every building should be specific to its
site and purpose the focus is not so much on the actual form, but rather on the performance of
the building, which is enabled through a set of passive and active strategies for energy-
efficiency. These can be translated from this project to any other building planned and
constructed in Oman.
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figure 01: site photo from April 2014
1.2. Climate
The climate at the location of the Eco House in Halban/Muscat, Oman is classified as a hot,
dry desert climate (2). The typical weather conditions can be roughly divided into two periods
changing over around the two days of equinox in March and September. In summer, the
monthly mean temperatures vary from 29.6°C to 35.0°C, but the maximum daily temperatures
can rise up to 49.2 °C. Even night hours can be as hot as 35°C, which is far beyond the
comfort range. During summer the humidity ratio is always above the comfort threshold of
11.5 g/kg for conditioned indoor spaces. In winter, the temperature is pleasant with monthly
mean temperatures between 21.1°C and 29.3°C. Temperatures might occasionally rise, but
never to extreme levels. In this period the humidity ratio typically varies between 7 and
13g/kg with temporary peaks of 15g/kg. For naturally conditioned spaces such humidity ratios
are still in an acceptable range. Rain events in Muscat are rare and of short duration. The data
shows that the climate at the Eco House site differs from the typical desert climate as it has a
generally higher humidity, and lower diurnal temperature variations due to the proximity to
the coast. (3)
1.3. Design
The conclusions from these settings for the design of the Eco Houseas a net-zero-energy
building are: a) prolonging the passive operation period without the need for mechanical
cooling through maximizing so-called passive design strategies; b) reducing the energy
demand for the mechanical cooling period through maximizing so-called active design
strategies; c) using the building to demonstrate cyclical processes for the use of water,
materials, local products, native plants, and for the education of students and the wider public
on sustainability in building.
2. PASSIVE STRATEGIES
The set of passive strategies aims at prolonging the passive operation period without the need
for mechanical cooling through maximizing so-called passive design strategies
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2.1. Compact Volume
The form of a building affects the amount of heat gained from insolation. The Eco House’s
form is based on a cylinderical volume. Compared to a cubic volume of the same size - a
shape that is widely used for a standard villa in Oman - two advantages are apparent. First, the
surface-to-volume ratio of the cylinder is only 92% of that of the cube. Furthermore, the solar
‘stress‘ on the building‘s envelope is not only factored by its size, but also by its form. A
round facade receives less solar radiation than a rectangular facade since only a minimal area
is directly exposed to the full impact of the sun, while all other areas are at a steeper angle and
thus yield less insolation. A study of the total annual solar exposure of the two building
volumes with the simulation programme Ecotect shows that a cubic building volume with the
dimensions of a standard villa located in Muscat receives 483,214 kWh/a on its surface, while
under the same circumstances the same volume but in a cylindrical form with the dimensions
of the Eco House receives only 336,160 kWh/a (figure 02). Due to its form alone, the Eco
House receives 30% less solar radiation compared to a standard villa in Oman. (4)
figure 02: solar exposure of the cylindrical volume of the Eco House, view north-west
2.2. High-performance Envelope
The opaque and glazed facades of the Eco House are designed for high-performance
regarding heat transmission, solar gains and air-tightness.
The selection of materials to construct the opaque walls is based on a study of the cooling
demand in relation to the envelope's performance through a one-zone thermal model of the
building with the programme WUFI (5). A comparison of the performance of the standard
wall construction in Oman (200mm concrete blocks) as a benchmark to the traditional wall
assembly (600mm mud-bricks) and an insulated cavity wall (200mm concrete blocks, 200mm
insulation, 200mm mud-bricks) shows that the insulated cavity wall can reduce the cooling
demand by 90% versus standard wall construction. The opaque walls of the Eco House are
now constructed from outside to inside of a 190mm lightweight concrete-pumice block, a
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200mm loose infill of perlite, and a 210mm sun-dried compressed earth brick. The heat
transfer coeficient is at U(wall) = 0.13 W/(m2*K), which is below the Passivhaus standard.
For the glazed walls a thermal single zone simulation with TRNSYS (6) was carried out. It
shows that the use of triple (ug=0.7 W/m²K) versus double glazing (ug = 1.1 W/(m2*K)) with
the same SHGC of 0.44 does actually not reduce annual electric energy use significantly
(figure 03). However, the aim for the glazing performance is to maximize daylight
transmission (Tvis) and minimize solar gains (SHGC) which is provided by high-selective
glazings. Finally the selected facade system is a curtain wall system with a ug=1.1 W/(m2*K),
Tvis, North=0.73, Tvis, South=0.52 SHGCNorth=0.41 / SHGCSouth=0.27, and a frame performance of
uf=0.8. Shading for the south façade is provided by fixed horizontal louvers with a cut-off
angle of 45°.
figure 03: Energy assessment of central bedroom
Air-tightness is another important factor for the high-performance envelope. The summer in
Muscat is hot and humid and infiltration has to be limited to reduce latent and sensible
cooling demand. The performance requirement for envelope air tightness is 0.1 ACH. A
vapour barrier is applied on the inner side of the outer block of the cavity wall and connected
seamlessly to the window frames of the curtain wall system.
2.3. Optimal Orientation
Not only the façade performance but also the orientation of the openings impacts the energy
balance. Based on the sun path on site, the openings in the façade were placed such that no
direct sunlight reaches the glazed walls. The circlular opaque wall is cut open along the lines
of sunrise and sunset on the longest day of the year. Within this cut, all large openings are
located facing north. Small shaded vertical opening to the south are necessary for daylight,
view connection and natural cross ventilation. The east and west facades are fully opaque.
Figure 04 shows the sun view study for an hourly sequence viewing the building from sun
position on the 12/21, 3/21 and 06/21. Everything that is visible receives direct solar
exposure, while everything not visible in the graph is in the shade.
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figure 04: sun view study of the ECO HAUS
The goal of the building’s design is to create a well-balanced use of daylight throughout the
building while reducing solar gains to a minimum and allowing a visual indoor-outdoor
connection. Figure 05 shows the daylight factor distribution at working height at the ground
and first floor of the building, indicating a homogeneously well daylit environment, achieving
illuminance targets even at sky conditions with 10 000 lux on the horizontal plane.
figure 05: daylight study of the ECO HAUS
2.4. Natural Ventilation
The main openings of the Eco House are exposed to the prevailing wind direction from north
north-east. The north facade is equipped with manually operated windows while the south
windows which reach all the way to the top of the double height facade are motorized so that
natural cross ventilation can be allowed for without compromising on safety.
2.5. Thermal Zoning
The guestrooms, dining and living room are situated at the north façade. The space between
the round opaque wall facing south and north conditioned unit is double-height and is used as
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a circulation space buffer zone where higher room temperatures are allowed. The ventilation
path also follows this strategy, where fresh air is supplied to the bedrooms and transferred into
the circulation spaces.
3. ACTIVE STRATEGIES
The set of active strategies aims at reducing energy demand for the mechanical cooling period
through maximizing so-called active design strategies.
3.1. Hydronic Cooling
Typical cooling systems in Oman are based on air-conditioning, with the downside of draft,
subcooling and high-energy intensity. In contrast the approach taken in the Eco House
separates the systems of providing air quality and room temperature control. All rooms are
cooled by water based radiant panels as part of the suspended ceilings. This shift from air to
water as a cooling medium (hydronic system) makes the system more energy-efficient and
provides a highly comfortable, draft free cooled environment. In total an active cooling area
of 100m2 is installed in the Eco House with a total cooling power of 6.0 kW. The system
operates with a supply temperature of max. 18°C, a return temperature of 21.5°C and a
surface temperature of ~22.5°C. Zones of individual temperature control are divided
according to the use: individual bedrooms, living/dining, kitchen, double-height common
space), allowing occupancy controlled operation of the system. It is important to note that the
proposed system is not a standard in this region and requires additional effort in instructing
installation and operation, even though the components are off-the shelf technology. This
makes the system potentially more expensive.
3.2. Energy Recovery
A radiant cooling system requires room dew point temperatures below water supply
temperature to avoid risk of condensation. Thus outdoor air supply has to be dehumidified to
ensure cooling operation. A dedicated outdoor air system (DOAS) provides a dehumidified
outdoor air rate of 600 m³/h distributed to the bedrooms and living room.. From there room
air passively transfers to the common space (second use of air) and finally is pulled from the
kitchen back to the air handling unit. The air-handling unit is equipped with a total energy
wheel for sensible and latent heat recovery. The wheel transfers the cooling potential of the
kitchen return air (25°C°, 10.11g/kg) passively to the entering outdoor air (46°C°, 20.7g/kg)
which after the wheel is at 30°C, 13.2 g/kg and thus significantly reduces sensible and latent
cooling load and energy demand. This is especially energy efficient during times where the
coefficient of performance (COP) of the chiller is lowest due to high outdoor temperatures.
Behind the cooling coil the supply air leaves the air handling unit with 12°C°and 8.73g/kg. It
is imperative to note that the limited dehumidification potential of a DOAS system providing
hygienic ventilation rates only in combination with a radiant cooling system requires a high
performance air-tight building envelope. This requires a precise and on-going quality
management process during the construction phase. Furthermore, since cooling loads
provided by this system are limited to surface area, the building loads (solar, internal,
transmission) need to be reduced first by passive strategies.
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3.3. Efficient Equipment
The household appliances for the Eco House such as fridge, freezer, cooker, dishwasher, and
washing machine as well as lighting, and also the chiller were selected on the criteria of
maximizing energy-efficiency. Because cooling is the main driver of energy consumption
(figure 03), special effort was taken to optimize chilled water production. The chilled water
supply temperature is increased to 10°C to improve the COP of the 15 KW chiller. The Air
handling units cooling coil is supersized to work with 10/18°C chilled water temperature.
Water returníng at 18°C directly feeds into the chilled ceiling system, returning at 21°C back
to the chiller. By increasing chilled water supply temperatures from 6/12°C to 10/21°C at
outdoor design conditions (46°C°, 20.7g/kg) the COP of the chiller is increased by 66% from
1.5 to 2.5. Additonally the use of two chilled water storage tanks of 1m³ each allows for the
operation of the chiller during the cooler night hours to increase its COP and thus decrease the
electricity demand of chilled water production.
3.4. Building Management System
The building management system ensures a proper control and operation of the active
building components to maintaining a high comfort indoor climate at minimized energy
demand. . In addition to monitoring energy use and production as well as indoor climate
conditions, the building management system optimizes the energy efficient operation of the
chiller-storage-system. Furthermore, the chilled water supply temperature to the radiant
systems is controlled to 2K above the monitored dew point conditions within the building to
reduce the risk of condensation.
3.5. Solar Power
In Oman solar power as a renewable source of energy is not yet widely used, despite the very
high potential for such technologies. The annual average insolation on a horizontal surface in
Halban, Oman (Latitude N 20° 23‘, Longitude E 55° 96‘) is at 2,241.1 kWh/m2/year and
among the highest in the world (3). On the roof of the Eco House a photovoltaic system with
38 modules of 327 Wp each has been installed at a tilt angle of 25°. The total array capacity
of 12.42 kWp has the potential to generate 20 MWh/a electricity based on the available
climate data. In addition, a roof installed solar thermal system with 4m2 panel area will cover
100% of domestic hot water demands with 55- 60°C hot water from a 200l tank. The Eco
House will be connected to the campus grid, and as long the university grid consumes more
electricity than the PV system can generate, it can feed into the grid. The Eco House is the
first residential building in Oman to receive permission from the Authority for Electricity
Regulation to feed in PV generated electricity and even receives a feed-in tariff that is equal
to the market price.
4. CONCLUSIONS
The Eco House project is a starting point in the development of energy-efficient buildings in
Oman. The focus of the evaluation should be, firstly, on monitoring the impact of the design-,
construction-, and technology-related strategies on the overall performance of the house, and
secondly, on weighing the economic viability of introducing such strategies on a wider range.
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4.1. Net-Zero-Balance
Based on simulations during the design phase and indoor temperature measurements during
the construction phase it is assumed that a net-zero-energy balance can be achieved for the
Eco House. An estimated electricity production of 20,000 kWh/a by the PV system represents
the upper limits of the Eco House’s annual energy consumption. Through the impact of the
passive strategies the cooling period can probably be shortened to five months per year (May-
September). Thermal simulations show that through the effecitiveness of the active strategies
a mean monthy electricity consumption of less than 4,000 kWh is a realistic expectation.
4.2. Market Viability
From an economic perspective, the Eco House is not competitive under the current market
conditions in Oman, which has distorted prices. Extremely high subsidies for electricity
encourage consumption and discourage conservation of energy. This in turn reduces the
availability of materials and products to improve energy-efficiency and increases their costs.
However, it can be argued that the passive strategies, which already have a high impact, are
within feasible economic limits. To implement them certain agility in design (volume,
orientation, ventilation, zoning) is needed, which would raise design costs. Additionally more
attention to construction methods (insulation, air-tightness) is necessary, which would raise
the building costs. The set of active strategies requires far more sophisticated technologies
and skills, which are not yet available in the local market, and thus are probably too costly for
the time being to be used on a larger scale.
4.3. Evidence-Based Policy Recommendations
In sum, the design and energy performance of the Eco House is promising and once the
operation has been monitored and evaluated, it will certainly be possible to improve and
simplify the components even further. However, the key to competitiveness lies on the
economic side. Only if the distortion of market prices is changed from subsidising inefficient
energy consumption caused by low-quality buildings and ineffective technologies, to
supporting energy conservation through effective design and construction quality, can the
costs for the Eco House or similar projects become competitive. Such policy changes need to
be evidence-based to precisely know, which measures will be most effective. The Eco House
project can serve as a starting point to gather such evidence as a step towards change.
REFERENCES
(1) Authority for Electricity Regulation in Oman (2014). Scoping Study on Electricity
Consumption in Residential Buildings in Oman
(2) http://en.wikipedia.org/wiki/Köppen_climate_classification
(3) Climate Data Software Meteonorm 6.0 - http://meteonorm.com/
(4) Ecotect study carried out by Wilfried Hofmann, www.baupluspartner.com
(5) WUFI PLUS 2.5 - http://www.wufi.de/index_e.html
(6) TRNSYS 17 - http://www.trnsys.com
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ResearchGate has not been able to resolve any citations for this publication.
(4) Ecotect study carried out by Wilfried Hofmann
Authority for Electricity Regulation in Oman (2014). Scoping Study on Electricity Consumption in Residential Buildings in Oman (2) http://en.wikipedia.org/wiki/Köppen_climate_classification (3) Climate Data Software Meteonorm 6.0-http://meteonorm.com/ (4) Ecotect study carried out by Wilfried Hofmann, www.baupluspartner.com (5) WUFI PLUS 2.5-http://www.wufi.de/index_e.html (6) TRNSYS 17-http://www.trnsys.com ISBN: 978-84-697-1815-5